1. Field of the Invention
The present invention relates to the packaging of perishable products, particularly shelf products such as meats, which are transported from an original packaging facility to a local retail outlet for purchase by the consumer with the prospect of home freezing.
2. Description of the Prior Art
Perishable products, especially meats, are generally cut and packaged at a slaughterhouse or other processing facility preparatory to shipment to various retail outlets. These meat products are commonly packaged in the normal oxygen-nitrogen atmosphere naturally occurring in such processing facilities. Exposure and packaging of perishable products in an ordinary oxygen-nitrogen atmosphere, however, eventually results in spoilage, both from bacterial decay, and in the case of red meat, from the conversion of myoglobin meat pigment to the grey or brown metmyoglobin, which color change renders the meat unacceptable to the average consumer. However, if air circulation around the product is limited or excluded, other generally undesired anaerobic phenomenon occurs, and meat loses its red color. This is because exposure to oxygen at temperatures above freezing is desirable for meat in order to oxygenate the meat pigment to bright red oxymyoglobin. The presence of this red oxymyoglobin produces the red "bloom" which is often desired by the consumer of such meat products.
Fresh meat is considered more desirable by many consumers if it is allowed to age for a period of days. It is known that an acceptable method of aging fresh meat is by vacuum packaging. Another acceptable method of aging fresh meat is packaging in an inert gas atmosphere such as a nitrogen gas atmosphere.
It is also known in the art to package perishable products in an atmosphere which inhibits bacterial growth, such as carbon dioxide.
It is also known in the art to vacuum package perishable products in order to extend their overall shelf life.
It is also known in the art that bacterial growth may be inhibited by packaging red meat in an atmosphere containing enriched oxygen and carbon dioxide. Alternatively, it is known in the art that the formation of oxymyoglobin over metmyoglobin may be achieved by packaging red meat in an atmosphere of pure or enriched oxygen.
Packaging may thus be designed to encourage maximum exposure of the surface of the packaged product to a modified atmosphere, thus significantly extending the shelf-life of the product and reducing wastage through spoilage, both of which are advantages to the retailer. Packaging may also be designed to encourage maximum exposure of the packaged product to a second atmosphere so as to enhance its aesthetic appeal and thus its marketability to the consumer.
An example of a package designed to take advantage of these known principles is seen in U.S. Pat. No. 4,055,672. In this patent, a perishable meat product is wrapped with a gas permeable membrane and is then sealed in a gas impermeable package while in the presence of an inert atmosphere. When display of the product is desired, the impermeable cover of the package is removed, thus allowing oxygen to reach the meat product, thereby producing the red "bloom" desired by consumers of such products.
Disadvantages associated with this package design include its inability to enable the retailer to retard or slow the deterioration of the fresh product once the impermeable cover is removed from the package. When the internal wrapped contents are exposed to a normal oxygen-nitrogen atmosphere, the meat undergoes a declining state of freshness and normally enjoys a maximum shelf life of about three days. Thus, if a retailer incorrectly assesses the demand for a given meat product, the unsold product declines in freshness and must either be sold at a reduced price or thrown away.
It is increasingly common for the consumer to freeze perishable products bought fresh in supermarkets or similar outlets in order to extend their relative shelf life. When such products are frozen, however, exposure to air or other gaseous atmospheres causes discoloration through dehydration, or so called "freezer burn". This renders the food less attractive and adversely affects its quality. The packaging described above, which is designed to increase exposure to the atmosphere in the package, is therefore highly unsuitable for the purpose of freezing. If the consumer places such packaging in a home freezer, freezer burn almost inevitably results. In order to avoid freezer burn, the consumer often must completely repackage this product at home, which is time consuming and oftentimes inconvenient. The result of these disadvantages has been that this type of packaging, while it reduces waste and is otherwise advantageous to the retailer, has not found general consumer acceptance in applications where home freezing is desired.
Packaging designed to specifically address the problem of "freezer burn" normally involves vacuum packing the perishable product between two impermeable membranes which are then thermosealed to form an air tight unit. Disadvantages associated with this type of system include the generally increased cost and inconvenience associated with the packaging, exhibition and repackaging of the product prior to home freezing. If a meat product is vacuum packed at the original processing facility, the product retains a generally purplish color since no oxymyoglobin is formed due to a lack of oxygen. This color is sometimes unacceptable for domestic retail marketing, resulting in the product being removed from the vacuum packaging prior to display and repackaged in a method allowing a gas atmosphere with enough oxygen for "bloom" to occur. If a consumer then desires to subsequently freeze the product, the meat product must again be securely packaged in a fashion to minimize the presence of free gases, this repackaging process resulting in a duplication of effort, waste of materials, and higher production costs.